1. Field of the Invention
It is an object of this invention to provide a method for preparing metal salts of unsaturated, short-chain carboxylic acids by reaction of unsaturated carboxylic acids with metal alcoholates. Furthermore, the uses of metal salts of unsaturated, short-chain carboxylic acids are also an object of this invention.
2. Description of the Prior Art
The homologues of mono-unsaturated carboxylic acids have the general empirical formula CnH2n-1, —COOH. These colourless liquids, when short-chained, are water-miscible at any ratio and tend to polymerize to form a glassy mass. The metal salts of acrylic acid, too, are colourless. They can be produced in solution or as a powder.
Methods for preparing aluminium salts of acrylic acid are known per se. For example, JP 48091012 describes the preparation of aluminium acrylate and the basic (or complex) salts thereof by reaction of Al(OH)3 gel or basic aluminium sulfate obtained as an insoluble salt from an aqueous solution of Al2(SO4)3 by eliminating all or part of the SO42−, with pure acrylic acid or a mixture of acrylic acid and an organic or inorganic acid. However, the formation of salts, which contaminate the product or need to be separated by a laborious separation step, is a disadvantage of said method.
The preparation of carboxylic acid metal salts has also been disclosed in U.S. Pat. No. 3,957,598. As reported, a metal salt of a carboxylic acid is formed by contacting a carboxylic acid with an activated metal. The activated metal is formed by combining a first metal with a second metal, which has an affinity for hydrogen in the presence of a proton source. Activated aluminium from a highly pure aluminium rod is caused to react with an alloy of gallium and indium in the presence of hydrochloric acid. The addition of excess water in the presence of the carboxylic acid and activated metal forms a polymeric metal salt from a water-soluble carboxylic acid.
It is a disadvantage of said method that an alloy of aluminium metals is required, which comprises components part of which are highly precarious in environmental aspects and can only be recovered by very expensive separation techniques.
U.S. Pat. No. 3,923,716 describes the preparation of aluminium acrylate in two steps. First, acrylic acid is added to aqueous sodium hydroxide to form sodium acrylate, which then is caused to react with aluminium trichloride to form (mono-, di-, tri-) aluminium acrylate and sodium chloride. Since the aluminium acrylate is poorly soluble, it can easily be separated from the dissolved sodium chloride and the aqueous reaction mixture. The disadvantage of said method, however, is the large quantity of hydrochloric acid which is dissolved in water and partially contaminated with product and needs to be disposed of.
The preparation of the corresponding salts of titanium is known from U.S. Pat. No. 5,998,646. However, the continuous feeding of oxygen for the reaction and a certain degree of O2 saturation has not been disclosed therein. On the contrary, the reaction is carried out at reduced pressure, with exclusion of air, and at elevated temperature, so that the absence of oxygen and a solvent atmosphere can be expected.